Phase-controlled group antennas are known, for example, from mobile communications technology.
Mobile communications antennas are normally used for base stations and consist of one or more columns arranged side by side, in each of which a plurality of radiators or sub-groups of radiators are arranged above one another. The radiators may be single polarised or dual polarised radiators. The antennas may be formed as mono-band, dual-band or as multi-band antennas which comprise radiators which can transmit and receive in a plurality of frequencies or frequency ranges (frequency bands). In terms of the structure of such group antennas as well as radiators and radiator arrangements, reference is made in this regard to previously known solutions, for example to prior publications WO 00/39894 A1, DE 197 22 742 A1, DE 198 23 749 A1, DE 101 50 150 A1 or, for example, U.S. Pat. No. 5,710,569.
Since, in a mobile communications system, the number of available channels is limited, the same frequencies are used again at specific distances. The range of a base station, defining a “mobile communications cell”, is therefore to be limited so that the cells of the mobile communications system do not disturb one another, that is to say are not subject to interferences.
It is therefore known to set the group antennas for such base stations with a different downtilt angle depending on requirements.
Whilst in the early days of mobile communications technology this downtilt angle could be set in different ways by mechanical measures, systems are now preferred in which, for example, a different downtilt angle can be set remotely and, depending on requirements and traffic level, can also be changed constantly.
On this basis phase shifters and, more precisely, phase shifter systems are preferably used to control the individual radiators using different phase positions, whereby a different downtilt angle can be set electrically.
For example, it is thus known to use differential phase shifters, as are known in principle from EP 1 208 614 B1. An odd number of radiators or sub-groups of radiators can be controlled by such a single phase or multi-phase shifter, wherein a central radiator or a central radiator group is preferably fed directly without phase shift. For example, two radiators or radiator groups can be controlled at the outputs thereof by a differential phase shifter with different phase shift. If, in each case, two further radiators or sub-groups of radiators are to be controlled, again with increased propagation-time changes and therefore with different phase positions, a further single phase shifter is required in each case, or a multi-phase shifter is used, as proposed in accordance with EP 1 208 614 B1.
Instead of group antennas, which comprise at least one radiator or a radiator group and which are operated without phase shift, group antennas which comprise an even number of radiators or radiator groups and/or do not comprise a radiator group and are operated without phase shift are also considered in principle.
The use of a single phase shifter to control sub-groups of radiators can be inferred, for example, from U.S. Pat. No. 5,917,455 A.
WO 03/019723 A1 describes an adjustable antenna feed network comprising a phase shifter means which is constructed in such a way that identical phase differences can be generated at the ports leading to the radiators by a movable dielectric.
WO 02/35651 A1 also describes the use of phase shifters in which a dielectric is moved along a stripline. The shift path is always the same. However, since the effective dielectricity numbers are different, phase shifts which each have the same phase differences from one another can be performed at the radiator ports. A substantially straight wave front with a different downtilt angle can thus be produced.
The corresponding phase shifter elements which can be used with the same objective as explained above are also to be inferred as being known in principle from WO 96/37922 A1.
Lastly, an antenna arrangement for lowering a downtilt angle or for setting the direction of radiation of the primary beam in the azimuth direction is also to be inferred as being known from US 2005/0219133 A1. In this prior publication an antenna arrangement comprising a phase shifter assembly with use of differential phase shifters is described, wherein the outputs of a first phase shifter arrangement are connected to the inputs of a respective second phase shifter assembly in order to thus control the radiator elements. A further possibility of a phase shifter network according to the prior art is also described in this prior publication and comprises a phase shifter assembly which includes two circular-segment-shaped phase shifter line portions which are arranged concentrically and are fed by a common feed arm which can be pivoted in a pointer-shaped manner about a common centre point.
By contrast, as an improved variant the prior publication cited above suggests using phase shifters, the two outputs of each of which are directly connected to radiator elements. In other words, a single-stage construction is thus used which is provided a number of times for two radiator elements in each case. For an antenna arrangement comprising a plurality of radiators which are to be fed with different phases, different phase shifters are therefore used in each case and are controlled by means of a transmission drive in such a way that different phase delays can be set for the individual radiator elements or radiator groups. A specific ratio between the pivoting of the phase shifters, for example of 1:3, 1:3:5, 1:3:5:7 and so on, to achieve a correspondingly fixed predetermined phase delay value is to be maintained in accordance with the number of phase shifters used and the arrangement of the radiators. Tolerances of +/−5% are acceptable. In order to optimise a radiation pattern, for example in the form of secondary lobes, it may be desirable in an alternative embodiment to vary the aforementioned ratios.
However, the correspondingly different adjustment of a downtilt angle in order to change the size of a corresponding mobile communications cell does not always lead to the desired success since the secondary lobes are nevertheless also shifted by the tilting (downtilt) of the primary radiation lobe. For example, the situation may arise that the first secondary lobe above the primary beam direction arrives in the vicinity of the horizontal plane (or even therebeneath) with increasing tilting of the main beam direction, with the result that mobile communications devices and base stations then act as interferers from another coverage area. A low secondary lobe level would thus be desirable.
On the other hand, however, the antenna gain is also to be as high as possible so as to guide the available transmission power effectively to the desired coverage area. A high antenna gain means a high bundling of the energy. In terms of the feed of group antennas, it is known however from the specialist literature that the optimisation of the antenna gain is often accompanied by an increase in the secondary lobe level.
The object of the present invention is therefore to provide an improved method for operating a phase-controlled group antenna as well as an improved phase-controlled group antenna itself, in which the first secondary lobe above or adjacent to the primary lobe has the lowest possible level, in particular with substantial beam tilt (large downtilt angle) or large beam pivoting (in order to suppress interference) and/or generally has a maximum antenna gain with slight beam tilt (that is to say with large cell expansion and illumination) or with slight beam pivoting.
It is highly surprising that, within the scope of the invention, the aforementioned objectives can be achieved by relatively simple means which are almost mutually exclusive. A tilting of the level of the first secondary lobe above the primary lobe with a considerably lowered downtilt angle often results in the antenna gain not being of the desired magnitude with a less pronounced adjustment of the tilting angle of the antenna gain or, conversely, in the level of the first secondary lobe above the primary lobe proving to be too great when optimising the antenna gain when tilting the primary lobe of the radiation diagram of the antenna (lowering the downtilt angle).
With the beam shaping by electronic means, the radiation diagram could now be changed in a relatively versatile manner, more specifically with free selection of the amplitudes and the phases. However, in particular in base station antennas for a mobile communications system, efficiency and price may be key factors. For this reason, mechanical phase shifters are generally often used for such antenna systems to adjust the downtilt angle differently. These mechanical phase shifters can directly extend the line length in a feed line (“Posaunen” principle, in which the entire line path can be reduced or increased by moving a line path). It is also possible to change the diffusion rate of the electromagnetic wave over a line path, for example by inserting a dielectric material in the region of the line path and thus changing the electrical conditions, or else a movable or displaceable coupling point can be used which can be displaced along a fixed line so as to shift the point of engagement. The possibilities for jointly changing the individual signals are considerably limited in this case, however.
Within the scope of the present invention a path is proposed which nevertheless offers the possibility of obtaining a much improved result in terms of solving the stated problem with minimal effort.
The principle of the invention is based on the fact that the radiators or radiator sub-groups arranged farthest away in a group antenna (for example in a group antenna the uppermost and lowermost radiators or radiator sub-groups) or controlled with the greatest phase difference are subjected to an additional phase shift, in other words are controlled by a disproportionately high phase shift in contrast to conventional systems.
In accordance with the invention, this does not occur with an additional means for generating an additional shift, but instead a correspondingly disproportionate phase shift with an additional phase shift proportion is generated by the same phase shifter which is also otherwise responsible in principle for beam pivoting.
Alternatively and in addition, in contrast to conventional systems, it is also possible to operate the radiators or radiator sub-groups which are arranged in a group antenna in the central region most densely in relation to one another (controlled by a differently adjustable phase position) using a disproportionately low phase shift with adjustment of a downtilt angle or an amended beam angle so that, in particular, the ratio of the phase position between the radiators operated with the greatest phase shift to the radiators operated with the lowest phase position change is characterised by a disproportionately large value.
This can be achieved when using a multiple differential phase shifter, as is known in principle for example from EP 1 208 614 B1, in that the outermost stripline, generally shaped in the arc of a circle, for feeding the farthest radiator or radiator sub-group lies further away from the concentric centre of a correspondingly pivotable, pointer-shaped tapping element and/or lies closer to the feedline centre, that is to say the pivot axis of the feedline arm at the next, arc-shaped stripline of this pivot axis.
In essence, this principle applies to an antenna system having an even or odd number of radiators and/or radiator sub-groups. An antenna system having an odd number of radiators or radiator groups is a system in which at least one radiator or at least one radiator group is provided which is fed with a bypassing of a differently adjustable phase shift system without changeable phase shift (normally arranged in the central region of the group antenna) so that no phase change is experienced at this radiator or this radiator group when the primary beam direction is pivoted (different adjustment of the downtilt angle).
An even radiator system is a system in which a group antenna having an even number of radiators or radiator sub-groups is provided (or, naturally, in this case a mixed system thereof) which are fed via the phase shift system, that is to say in particular do not comprise a central system which is controlled without phase shift.
In a supplementary or alternative embodiment of the invention it is also possible to position the pivot axis of the generally pointer-shaped, pivotable phase shift adjustment element closer to the striplines shaped as a segment or arc of a circle so that this pivot axis lies closer to the striplines than the centre point of the circular-segment-shaped striplines. As a result, a disproportionately large change in propagation time is generated by the farthest circular-segment-shaped stripline portion at the opposing connection points, and the phase shift change and therefore the propagation time change is reduced proportionately at the innermost circular-segment-shaped stripline portions, whereby the success according to the invention is achieved.
In particular, the invention is specifically based on the fact that at least one radiator or at least two pairs of radiators or radiator sub-groups fed via a differential phase shift are operated with an additional phase shift compared to the other radiators or radiator sub-groups in terms of the transmitting or receiving signal, which has a positive effect on an additional beam shaping within the meaning of the invention. The contribution of the additional phase shift is dependent on the adjustment of the beam pivoting. Owing to the fact that the most simple additional beam deformation is to be achieved, it is ensured that the size of the secondary lobe located above the primary lobe is smaller in the tilted state with increasingly advanced tilting of the primary lobe of a group antenna compared to a system not according to the invention (interference with adjacent cells is thus avoided) and/or that the antenna gain of this primary lobe is relatively greater in the case of a primary lobe oriented in the horizontal direction (that is to say with a tilting or pivoting angle which is not so pronounced) than with conventional antenna systems.
The example non-limiting technology herein provides illustrative non-limiting advantages and features at least some of which are:                with an antenna array having an even number of radiator arrangements (1) and/or without a phase-neutrally controlled central radiator arrangement (1x), the following inequality is satisfied:PhN: Ph1≧SN:S1+0.4        with an odd number of radiator arrangements (1) and/or a phase-neutrally controlled central radiator arrangement (1x), the following inequality applies:PhN: Ph1≧SN:S1+k in which k is 0.25 or preferably 0.30 and in particular 0.40        with an even number of radiator arrangements (1) and/or without a phase-neutrally controlled central radiator arrangement (1x), the following inequality applies:PhN: Ph1≧SN:S1+k in which k is 0.5 or preferably 0.6 and in particular 0.8,        with an odd number of radiator arrangements (1) and/or a phase-neutrally controlled central radiator arrangement (1x), the following inequality applies:PhN: Ph1≧n+min which n is a natural number 2, 3, 4 . . . N, corresponding to the number of radiator arrangements (1) provided on an antenna array half above or below the centre (Z) of the antenna array, and m corresponds to 2.0 or in particular 1.5 or 1.0,        with an even number of radiator arrangements (1) and/or without a phase-neutral centre feed of a radiator arrangement (1x) close to the centre, the following inequality applies:PhN:Ph1≦2n+m in which n is a natural number 2, 3, 4 . . . N, corresponding to the number of radiator arrangements (1) provided on an antenna array half above or below the centre (Z) of the antenna array, and m corresponds to 3.0 or preferably 2.5 or preferably 2.0.        
The example non-limiting technology herein provides illustrative non-limiting advantages and features some of which are:                with an antenna array having an even number of radiator arrangements (1) and/or without a phase-neutrally controlled central radiator arrangement (1x), the following inequality is satisfied:PhN: Ph1>SN:S1+0.4        the group antenna consists of an even number of radiator arrangements (1) and/or does not comprise a phase-neutrally controlled radiator arrangement (1x) provided in the region of the centre (Z) of the group antenna,        the group antenna is equipped in particular with an odd number of radiator arrangements (1) having a phase-neutrally controlled radiator arrangement (1x) arranged close to the centre or in the centre (Z) of the group antenna,        with an odd number of radiator arrangements (1) and/or a phase-neutrally controlled central radiator arrangement (1x), the following inequality is satisfied:PhN: Ph1>SN:S1+k in which k is 0.25 or preferably 0.30 and in particular 0.40,        with an even number of radiator arrangements (1) and/or without a phase-neutrally controlled central radiator arrangement (1x), the following inequality applies:PhN: Ph1>SN:S1+k in which k is 0.5 or preferably 0.6 and in particular 0.8,        with an odd number of radiator arrangements (1) and/or a phase-neutrally controlled central radiator arrangement (1x), the following inequality applies:PhN: Ph1<n+m in which n is a natural number 2, 3, 4 . . . N, corresponding to the number of radiator arrangements (1) provided on an antenna array half above or below the centre (Z) of the antenna array, and m corresponds to 2.0 or in particular 1.5 or 1.0,        with an even number of radiator arrangements (1) and/or without a phase-neutral centre feed of a radiator arrangement (1x) close to the centre, the following inequality applies:PhN: Ph1<2n+m in which n is a natural number 2, 3, 4 . . . N, corresponding to the number of radiator arrangements (1) provided on an antenna array half above or below the centre (Z) of the antenna array, and m corresponds to 3.0 or preferably 2.5 or preferably 2.0,        at least the stripline portion (11, 11a) having the largest radius (RN) is provided with a dielectric, which is not air, on one or preferably on both sides, which dielectric is provided with constant or different or varying thickness over the entire length of the stripline portion or over one or over more partial lengths.        